Producing SOI structure using high-purity ion shower

ABSTRACT

Disclosed are methods for making SOI and SOG structures using purified ion shower for implanting ions to the donor substrate. The purified ion shower provides expedient, efficient, low-cost and effective ion implantation while minimizing damage to the exfoliation film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/444,741, filed May 31, 2006, the entiredisclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to processes for makingsemiconductor-on-insulator (“SOI”) structures. In particular, thepresent invention relates to processes for making SOI structures byusing high-purity ion shower implantation. The present invention isuseful, for example, in the manufacture of semiconductor-on-insulatorstructures such as silicon-on-insulator structures,semiconductor-on-glass structures such as silicon-on-glass structures,and related semiconductor devices.

BACKGROUND OF THE INVENTION

As used herein, the abbreviation “SiOI” refers to silicon-on-insulator.The abbreviation “SOI” refers to semiconductor-on-insulator in general,including but not limited to SiOI. The abbreviation “SiOG” refers tosilicon-on-glass. The abbreviation “SOG” refers tosemiconductor-on-glass in general, including but not limited to SiOG.SOG is intended to include semiconductor-on-ceramics andsemiconductor-on-glass-ceramics structures. Likewise, SiOG is intendedto include silicon-on-ceramics and silicon-on-glass-ceramics structures.

SiOI technology is becoming increasingly important for high performancethin film transistors, solar cells, and displays, such as active matrixdisplays. The SiOI wafers typically consists of a thin layer ofsubstantially single-crystalline silicon generally 0.1-0.3 microns inthickness but, in some cases, as thick as 5 microns, on an insulatingmaterial.

Various ways of obtaining such a SiOI wafer include epitaxial growth ofSi on lattice matched substrates; bonding of a single-crystalline waferto another silicon wafer on which an oxide layer of SiO₂ has been grown,followed by polishing or etching of the top wafer down to, for example,a 0.1 to 0.3 micron layer of single-crystalline silicon; orion-implantation methods in which either hydrogen or oxygen ions areimplanted either to form a buried oxide layer in the silicon wafertopped by Si in the case of oxygen ion implantation or to separate(exfoliate) a thin Si layer to bond to another Si wafer with an oxidelayer as in the case of hydrogen ion implantation. Of these threeapproaches, the approaches based on ion implantation have been found tobe more practical commercially. In particular, the hydrogen ionimplantation method has an advantage over the oxygen implantationprocess in that the implantation energies required are less than 50% ofthat of oxygen ion implants and the dosage required is two orders ofmagnitude lower.

Exfoliation by the hydrogen ion implantation method was initially taughtin, for example, Bister et al., “Ranges of the 0.3-2 KeV H⁺ and 0.2-2KeV H₂+Ions in Si and Ge,” Radiation Effects, 1982, 59:199-202, and hasbeen further demonstrated by Michel Bruel. See Bruel, U.S. Pat. No.5,374,564; M. Bruel, Electronic Lett., 31, 1995, 1201-02; and L.Dicioccio, Y. Letiec, F. Letertre, C. Jaussad and M. Bruel, ElectronicLett., 32, 1996, 1144-45.

The hydrogen ion implantation method typically consists of the followingsteps. A thermal oxide layer is grown on a single-crystalline siliconwafer. Hydrogen ions are then implanted into this wafer to generatesubsurface flaws. The implantation energy determines the depth at whichthe flaws are to be generated and the dosage determines flaw density.This wafer is then placed into contact with another silicon wafer (thesupport substrate) at room temperature to form a tentative bond.

The wafers are then heat-treated to about 600° C. to cause growth of thesubsurface flaws for use in separating a thin layer of silicon from theSi wafer. The resulting assembly is then heated to a temperature above1000° C. to fully bond the Si film with SiO₂ underlayer to the supportsubstrate, i.e., the un-implanted silicon wafer. This process thus formsa SiO₂ structure with a thin film of silicon bonded to another siliconwafer with an oxide insulator layer in between.

Cost is an important consideration for commercial applications of SOIand SiOI structures. To date, a major part of the cost of suchstructures has been the cost of the silicon wafer which supports theoxide layer, topped by the Si thin film, i.e., a major part of the costhas been the support substrate.

Although the use of quartz as support substrate has been mentioned invarious patents (see U.S. Pat. Nos. 6,140,209, 6,211,041, 6,309,950,6,323,108, 6335,231 and 6,391,740), quartz is itself a relativelyexpensive material. In discussing support substrates, some of theabove-references have mentioned quartz glass, glass, and glass-ceramics.Other support substrate materials listed in these references includediamond, sapphire, silicon carbide, silicon nitride, ceramics, metals,and plastics.

It is not at all a simple matter to replace a silicon wafer with a wafermade out of a less expensive material in an SOI structure. Inparticular, it is difficult to replace a silicon wafer with a glass orglass-ceramic or ceramic of the type which can be manufactured in largequantities at low cost, i.e., it is difficult to make cost effective SOGand SiOG structures.

Co-pending, co-assigned U.S. patent application Ser. No. 10/779,582,published as US2004/0229444 A1, describes techniques for making SiOG andSOG structures and novel forms of such structures. Among the numerousapplications for the invention are those in such fields asoptoelectronics, FR electronics, and mixed signal (analog/digital)electronics, as well as display applications, e.g., LCDs and OLEDs,where significantly enhanced performance can be achieved compared toamorphous and polysilicon based devices. In addition, photovoltaics andsolar cells with high efficiency were also enabled. Both the processingtechniques and its novel SOI structures significantly lower the cost ofan SOI structure.

Another factor significantly affecting the cost of ion-implantationapproach to producing SOI, SiOI, SOG and SiOG structures is theefficiency of the ion-implantation process. Traditionally, hydrogen ionimplantation or oxygen ion implantation were used, with the former beingpreferred due to the higher efficiency. However, those traditionalion-implantation processes require the use of narrow ion beams, whichlead to long implantation time and high cost. As a result, substituteion sources were developed and disclosed in the prior art.

For example, U.S. Pat. No. 6,027,988 proposes the use of plasma ionimmersion implantation (“PIII”), where the semiconductor substrate suchas a silicon wafer is placed in a plasma atmosphere and an electricfield, thereby enabling large area simultaneous ion implantation.However, PIII suffers from the drawbacks of surface charging and etchingby the plasma and lack of flexibility at higher energy, lack of accuratedosage control, and inability to precisely control the thickness of theion implantation zone and the thickness of the exfoliation film.

Another alternative to narrow area ion beam implantation is ion showerimplantation (ISI). An ion shower is typically a large area ion beamextracted from a plasma source by means of an extraction electrode andan optional post-acceleration system. Ion shower differs from PIII inthat it uses a remote plasma, a field-free region around the substrateto be ion-implanted, and a continuous instead of a pulsed ion beam.These features of the ISI system eliminates the surface charging andetching problem of PIII, and enables accurate dosage control.

The present inventors have discovered that, while ISI can achieve quickion implantation, the use of conventional ISI in the production of SOGstructures can lead to unacceptable damage of the thin film uponseparation thereof from the substrate. For the manufacture of manysemiconductor devices, it is important the integrity of the crystallinelattice of the thin film is substantially maintained during theimplantation and upon separation thereof from the substrate.

Therefore, there remains a process for separating a thin film ofsemiconductor material that is efficient, effective, yet withoutdamaging the desired structure of the thin film. In particular, thereremains a process for making SOG structures wherein the ion implantationprocess can be implemented with efficiency and efficacy.

The present invention satisfies this long-standing need.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, it is provided aprocess for forming a SOI structure comprising the following steps:

providing a donor substrate comprising semiconductor material having afirst donor external surface; and

implanting a plurality of ions belonging to a first species through thefirst donor external surface into an ion implantation zone at a depthbelow the first donor external surface by using a first ion showerpurified by electromagnetic separation such that the structure of atleast a 50 nm thick part, in certain embodiments at least a 100 nm thickpart, in certain embodiments at least a 150 nm thick part, in certainembodiments at least a 200 nm thick part, of the film of materialsandwiched between the ion implantation zone and the first donorexternal surface (“exfoliation film”) is essentially not damaged.

In certain embodiments of this process of the present invention, theexfoliation film comprises single-crystalline silicon.

In certain embodiments of the process of the first aspect of the presentinvention, in step (II), the depth of the ion implantation zone is lessthan about 1000 nm, in certain embodiments less than about 500 nm, incertain other embodiments less than about 300 nm, in certain otherembodiments less than about 150 nm, in certain other embodiments lessthan about 100 nm. In certain embodiments of this process, the thicknessof the non-damaged part of the exfoliation film is at least a majorityof (50%) of the total thickness of the exfoliation film, in certainembodiments at least 60%, in certain embodiments at least 80%, incertain embodiments at least 90%.

In certain embodiments of this process of the present invention, in step(II), the ion implantation zone has a thickness of not larger than about1 μm, in certain embodiments not larger than about 500 nm, in certainother embodiments not larger than about 300 nm, in certain otherembodiments not larger than about 200 nm.

In certain embodiments of this process of the present invention, in step(II), the first ion shower consists essentially of the ions belonging toa first species. In certain embodiments, the ions belonging to the firstspecies is a single ion species selected from H₃ ⁺, H⁺, H₂ ⁺, D₂ ⁺, D₃⁺, HD⁺, H₂ ⁺, HD₂ ⁺, He⁺, He²⁺, O⁺, O₂ ⁺ O₂ ⁺ and O₃ ⁺. In certainembodiments, the ions belonging to the first species are essentiallyfree of phosphorous, boron, arsenic, carbon, nitrogen, oxygen, fluorine,chlorine and metals.

Certain embodiments of this process of the present invention furthercomprise the following step (III) separate of and independent from step(II):

implanting a plurality of ions belonging to a second species through thefirst donor external surface into the ion implantation zone at the depthbelow the first donor external surface by using a second ion showerpurified by electromagnetic separation such that the structure of atleast a 50 nm thick part, in certain embodiments at least a 100 nm thickpart, in certain other embodiments at least a 150 nm thick part, incertain embodiments at least a 200 nm thick part, of the exfoliationfilm is essentially not damaged, said ions belonging to the secondspecies being different from the ions belonging to the first species.

According to certain embodiments of the first aspect of the presentinvention, the ion implantation zone comprises a first ion implantationzone where the ions belonging to the first ion species are implanted anda second ion implantation zone where the ions belonging the second ionspecies are implanted, and the first ion implantation zone and thesecond ion implantation zone substantially overlap. In certainembodiments, the distance between the peak of the ion species are lessthan about 200 nm, in certain embodiments less than about 150 nm, incertain embodiments less than about 100 nm, in certain embodiments lessthan about 50 nm.

In certain particular embodiments of this process of the presentinvention, the ions belonging to the first species are H₃ ⁺, and theions belonging to the second species are He⁺. In certain embodiments,the ratio of the energy of H₃ ⁺ ions to that of the He⁺ ions is about2:1. In certain particular embodiments of this process, the H₃ ⁺ has anenergy of about 60 KeV, and the He⁺ has an energy of about 30 KeV. Incertain advantageous embodiments, the H₃ ⁺ implantation zone and the He⁺implantation zone, both within the ion implantation zone of the donorsubstrate, overlap substantially.

In certain embodiments of the process according to the first aspect ofthe present invention, it further comprises a step (IIIA) separate fromand independent of step (II) as follows:

(IIIA) implanting a plurality of ions through the first donor externalsurface into the ion implantation zone at the depth below the firstdonor external surface by using a beam-line implanter.

In certain embodiments of the process according to the first aspect ofthe present invention, it further comprises a step (IIIB) separate fromand independent of step (II) as follows:

(IIIB) implanting a plurality of ions through the first donor externalsurface into the ion implantation zone at the depth below the firstdonor external surface by using a conventional ion shower.

Certain embodiments of the process of the first aspect of the presentinvention comprises the following step (IV):

bonding the first donor external surface to a recipient substrate.

Certain other embodiments of the process of the first aspect of thepresent invention comprises the following step (V):

separating at least part of the exfoliation film and at least part ofthe material in the implantation zone at a location within theimplantation zone.

Certain embodiments of the process of the first aspect of the presentinvention comprises the following (IV) and (V):

(IV) bonding the first donor external surface to a recipient substrate;and

separating the exfoliation film and at least part of the material in theseparation zone at a location within the implantation zone.

According to certain embodiments of the first aspect of the presentinvention wherein the donor substrate is bonded to a recipient substrateas described above, the recipient substrate is selected from the groupconsisting of: a semiconductor wafer with or without an oxide surfacelayer; a glass plate; and a glass-ceramic plate.

According to certain embodiments of the first aspect of the presentinvention wherein the donor substrate is bonded to a recipient substrateas described above, the recipient substrate is a silicon wafer with aSiO₂ surface layer, and the first donor external surface of is bonded tothe SiO₂ surface layer in step (IV).

According to certain embodiments of the first aspect of the presentinvention wherein the donor substrate is bonded to a recipient substrateas described above, the recipient substrate is a SiO₂ glass plate.

According to certain embodiments of the first aspect of the presentinvention wherein the donor substrate is bonded to a recipient substrateas described above:

the recipient substrate comprises oxide glass or oxide glass-ceramic;and

in step (IV), the bonding is effected by applying (a) forces to thedonor and recipient substrates such that they are pressed into closecontact; (b) electric field within the donor and recipient substratessuch that the electrical potential in the donor substrate is higher thanthat in the recipient substrate; and (c) a temperature gradient betweenthe donor and recipient substrates.

According to certain embodiments of the first aspect of the presentinvention, in step (II), the electromagnetic separation of the first ionshower is effected by magnetic means.

A second aspect of the present invention is a process for forming a SOIstructure comprising the following steps:

(A1) providing a donor substrate and a recipient substrate, wherein:

the donor substrate comprises a semiconductor material and a first donorexternal surface for bonding with the recipient substrate (first bondingsurface) and a second donor external surface;

the recipient substrate comprises an oxide glass or oxide glass-ceramicand two external surfaces: (i) a first recipient external surface forbonding to the first substrate (the second bonding surface); and (ii) asecond recipient external surface;

(A2) implanting a plurality of ions belonging to a first species throughthe first donor external surface into an ion implantation zone of thedonor substrate at a depth below the first donor external surface byusing a first ion shower purified by electromagnetic separation suchthat the internal structure of at least a 50 nm thick part, in certainembodiments at least a 100 nm thick part, in certain embodiments atleast a 150 nm part, in certain embodiments at least a 200 nm thickpart, of the film of material sandwiched between the implantation zoneand at least a majority of the first donor external surface(“exfoliation film”) is essentially not damaged;

(B) after steps (A1) and (A2), bringing the first and second bondingsurfaces into contact;

(C) for a period of time sufficient for the donor and recipientsubstrates to bond to one another at the first and second bondingsurfaces, simultaneously:

(1) applying forces to the donor substrate and/or the recipientsubstrate such that the first and second bonding surfaces are pressedinto contact;

(2) subjecting the donor and recipient substrates to an electric fieldhaving a general direction of from the second recipient external surfaceto the second donor external surface; and

(3) heating the donor and recipient substrates, said heating beingcharacterized in that the second donor and recipient external surfaceshave average temperatures T₁ and T₂, respectively, said temperaturesbeing selected such that upon cooling to a common temperature, the donorand recipient substrates undergo differential contraction to therebyweaken the donor substrate at the ion implantation zone; and

(D) cooling the bonded donor and recipient substrates and splitting thedonor substrate at the ion implantation zone;

wherein the oxide glass or oxide glass-ceramic comprises positive ionswhich during step (C) move within the recipient substrate in a directionaway from the second bonding surface and towards the second recipientexternal surface.

In certain embodiments of the second aspect of the present invention,the exfoliation film comprises single-crystalline semiconductormaterial.

In certain embodiments of the process of the second aspect of thepresent invention, in step (A2), the depth of the ion implantation zoneis less than about 1000 nm, in certain embodiments less than about 500nm, in certain other embodiments less than about 300 nm, in certainother embodiments less than about 150 nm, in certain other embodimentsless than about 100 nm. In certain embodiments of this process, thethickness of the non-damaged part of the exfoliation film is at least50% of the total thickness of the exfoliation film, in certainembodiments at least 60% of the total thickness of the exfoliation film,in certain embodiments at least 80% of the total thickness of theexfoliation film, in certain embodiments at least 90%.

In certain embodiments of the second aspect of the present invention,the exfoliation film comprises single-crystalline silicon.

In certain embodiments of the second aspect of the present invention, instep (A2), the ion implantation zone has a thickness of not larger thanabout 1 μm, in certain embodiments not larger than about 500 nm, incertain other embodiments not larger than about 300 nm, in certain otherembodiments not larger than about 200 nm.

In certain embodiments of the second aspect of the present invention, instep (A2), the first ion shower consists essentially of the ionsbelonging to a first species.

In certain embodiments of the second aspect of the present invention,the ions belonging to the first species is a single ion species selectedfrom H₃ ⁺, H⁺, H₂ ⁺, D₂ ⁺, D₃ ⁺, HD⁺, H₂D⁺, HD₂ ⁺, He⁺, He²⁺.

In certain embodiments of the second aspect of the present invention,the ions belonging to the first species are essentially free ofphosphorous, boron, arsenic, carbon, nitrogen, oxygen, fluorine,chlorine and metals.

Certain embodiments of the second aspect of the present inventioncomprises the following step (A3) separate of and independent from step(A2):

(A3) implanting a plurality of ions belonging to a second speciesthrough the first donor external surface into the ion implantation zoneat the depth below the first donor external surface by using a secondion shower purified by electromagnetic separation such that thestructure of at least a 50 nm thick part, in certain embodiments atleast a 100 nm thick part, in certain embodiments at least a 150 nmthick part, in certain embodiments at least a 200 nm thick part, of theexfoliation film is essentially not damaged, said ions belonging to thesecond species being different from the ions belonging to the firstspecies.

According to certain embodiments of the second aspect of the presentinvention, the ion implantation zone comprises a first ion implantationzone where the ions belonging to the first ion species are implanted anda second ion implantation zone where the ions belonging the second ionspecies are implanted, and the first ion implantation zone and thesecond ion implantation zone substantially overlap. In certainembodiments, the distance between the peaks of the first and secondspecies of ions is less than about 200 nm, in certain embodiments lessthan about 150 nm, in certain embodiments less than about 100 nm, incertain embodiments less than about 50 nm.

In certain embodiments, the ions belonging to the first species are H₃⁺, and the ions belonging to the second species are He⁺. The energy ofthe H₃ ⁺ and He⁺ are chosen such that upon implantation, they distributeessentially in the ion implantation zone. In certain embodiments, theratio of the energy of the H₃ ⁺ ions to that of the He⁺ ions are about2:1. For example, the H₃ ⁺ may have an average energy of about 60 KeV,and the He⁺ may have an average energy of about 30 KeV. In certainadvantageous embodiments, the H₃ ⁺ ions are implanted in a H₃ ⁺ ionimplantation zone, the He⁺ ions are implanted in a He⁺ ion implantationzone, both the H₃ ⁺ and He⁺ ion implantation zones are within the ionimplantation zone of the donor substrate, and they overlapsubstantially.

In certain embodiments of the second aspect of the present invention, instep (A2), the electromagnetic separation of the first ion-shower iseffected by magnetic means.

In certain embodiments of the second aspect of the present invention,the first bonding surface (the first donor external surface) is treatedto reduce the hydrogen concentration after ion implantation but beforeit is brought into contact with the first recipient external surface(second bonding surface) for bonding. Suchhydrogen-concentration-reducing means may be selected from oxygen plasmatreatment, ozone treatment, H₂O₂ treatment, H₂O₂ and ammonia treatment,H₂O₂ and acid treatment, and combinations thereof.

In certain embodiments of the process of the second aspect of thepresent invention, at the end of the process, the bond strength betweenthe recipient substrate and the exfoliation film is at least 8joules/cm², in certain embodiments at least 10 joules/cm², in certainother embodiments at least 15 joules/cm².

In certain embodiments of the process of the second aspect of thepresent invention, wherein in step (A2), the electromagnetic separationof the first ion shower is effected by magnetic means.

In certain embodiments of the process according to the second aspect ofthe present invention, it further comprises a step (A3.1) separate fromand independent of step (A2) as follows:

(A3.1) implanting a plurality of ions through the first donor externalsurface into the ion implantation zone at the depth below the firstdonor external surface by using a beam-line implanter.

In certain embodiments of the process according to the second aspect ofthe present invention, it further comprises a step (A3.2) separate fromand independent of step (A2) as follows:

(A3.2) implanting a plurality of ions through the first donor externalsurface into the ion implantation zone at the depth below the firstdonor external surface by using a conventional ion shower.

The present invention has the advantages of the traditionalnon-mass-separated ion shower ion implantation technique in that it iscapable of large area simultaneous ion implantation, low or no surfaceetch, high efficiency and low cost. By using purified ion shower, thepresent invention further avoids the damage and contamination that canbe caused by the traditional non-mass-separated ion shower to theimplanted semiconductor material. Therefore, the present inventionenables expedient, efficient and effective ion implantation that issuitable for the production of various SOI structures, including but notlimited to SiOI structures, particularly SOG structures, including butnot limited to SiOG structures.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from the description or recognizedby practicing the invention as described in the written description andclaims hereof, as well as the appended drawings.

It is to be understood that the foregoing general description and thefollowing detailed description are merely exemplary of the invention,and are intended to provide an overview or framework to understandingthe nature and character of the invention as it is claimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a schematic illustration of an embodiment of a donor substrateion-implanted using the process of the present invention.

FIG. 2 is a schematic illustration of another embodiment of a donorsubstrate ion-implanted using the process of the present invention.

FIG. 3 is a schematic illustration of a conventional non-mass-separatedion shower apparatus being used for ion-implanting a substrate.

FIG. 4 is a schematic illustration of an apparatus using the process ofthe present invention for ion-implanting a substrate where the ionshower is purified by a magnetic means.

FIG. 5 is a schematic illustration of an ion-implanted donor substratebeing bonded with a recipient substrate in the presence of an electricfield, temperature gradient and pressure.

FIG. 6 is a schematic illustration of the splitting of the structure ofFIG. 5 to form a SOI structure after the structure of FIG. 5 is cooledto a temperature of T₃.

FIG. 7 is a TEM image of a thin exfoliated silicon film obtained byusing conventional non-mass-separated ion shower, showing damages to thecrystalline structure thereof.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “semiconductor material” means a material, withor without additional modification such as doping, exhibitssemiconductive properties. Thus, for example, the semiconductor materialin the meaning of the present invention may be a pure single-crystallinesilicon, or silicon doped with phosphorous, boron, arsenic or otherelements. The semiconductor material is typically in the form of asubstantially single-crystalline material. The word “substantially” isused in describing material to take account of the fact thatsemiconductor materials normally contain at least some internal orsurface defects either inherently or purposely added, such as latticedefects or a few grain boundaries. The word “substantially” alsoreflects the fact that certain dopants may distort or otherwise affectthe crystal structure of the bulk semiconductor.

As used herein, term “first ion implantation zone” means a zone in thedonor substrate which, upon implantation, has the peak local density ofthe implanted ions belonging to the first ion species in terms of numberof ions per unit of volume located in the middle thereof, and comprisesat least 50% of the implanted ions belonging to the first species. Theterm “second ion implantation zone” means a zone in the donor substratewhich, upon implantation, has the peak local density of the implantedions belonging to the second ion species in terms of number of ions perunit of volume located in the middle thereof, and comprises at least 50%of the implanted ions belonging to the second species. By “substantiallyoverlapping,” it is meant that the first ion implantation zone and thesecond ion implantation zone have an overlap of at least 50%. For adonor substrate ion-implanted with a single species of ions, the ionimplantation zone of the overall substrate is the first ion implantationzone. For a donor substrate ion-implanted with a first and a secondspecies, and even more species of ions, the ion implantation zone of theoverall substrate is the combination of the first ion implantation zone,the second ion implantation zone and additional ion implantation zones,if any. The overall ion implantation zone can be predetermined by oneskilled in the art in light of the teachings of the present application.

In the present application, a species of ions has a specific mass andcharge. Thus any ion with either a differing mass or change is adifferent species. For example, H⁺, H₂ ⁺, H₃ ⁺, D⁺, D₂ ⁺, D₃ ⁺, HD⁺,H₂D⁺, HD₂ ⁺, He⁺, He²⁺ are all different species of ions in the presentapplication.

Electromagnetic separation in the present application means separationof the different species of ions by means of subjecting the ions toelectric and/or magnetic field(s).

The present invention can be applied to the production of any SOIstructures. The following detailed description of the present inventionuses the production of SiOI for illustration purpose. It should beunderstood that the present invention is not limited to the productionof SiOI structures.

The present invention can be applied to the production of any SOGstructures. The following detailed description of the present inventionuses the production of SiOG for illustration purpose. It should beunderstood, however, that the present invention is not limited to theproduction of SiOG structures. Production of SiOG by using the method ofthe present invention constitutes one aspect of the present invention.Co-pending, co-assigned U.S. patent application Ser. No. 10/779,582, nowpublished as US 2004/0229444 A1, describes means for making SOGstructures, particularly SiOG structures, and novel forms of suchstructures, the disclosure of which is incorporated herein by referencein its entirety.

Ion implantation is one of the most expensive steps in the production ofSOI structures. In SOG structures, the use of inexpensive substratematerials, such as glass and glass-ceramic materials, can reduce theoverall cost of the SOG significantly. In the manufacture of SOGstructures, as is disclosed in US 2004/0229444 A1, hydrogen ionimplantation can be used to separate a thin film semiconductor materialsuch as single-crystalline silicon from a donor substrate. Traditionalbeam-line ion implantation method and equipment may be used for thispurpose. However, the use of traditional beam-line ion implantationequipment is very expensive. In fact, such film separation processgenerally requires large doses of hydrogen ions. For beam-lineimplanters, it often takes a long time to achieve the desired level ofimplantation. This significantly increases the manufacture cost of theSOG structures. Moreover, the use of beam ion hydrogen implantationtypically results in a film separated from the donor substrate andbonded to the recipient wafer that is thicker than desired. Furtherpost-treatment, including thinning and polishing of the thick film isrequired for many intended applications, adding to the overall processcomplexity, lowering productivity and yield, hence increasing the costof end product.

As discussed supra, alternative ion implantation method and equipmentwere proposed in the prior art to replace beam-line ion implantation.U.S. Pat. No. 6,027,988, the relevant portion thereof is incorporatedherein by reference, discloses the use of plasma immersion ionimplantation (PIII) for that purpose. In the PIII method, a plasma isgenerated, the recipient wafer is placed inside the plasma and electricfield, such that a plurality of ions are accelerated by the electricfield and implanted into the donor substrate. This method suffers fromsurface etch of the donor substrate and difficulty in dosage control. Inaddition, because multiple species of ions are generated and present inthe plasma, and the ions when implanted tend to have wide distributionof energy levels, the implantation depth, hence the thickness of thefilm to be separated is difficult to control. Still further, detrimentalcontaminant ions in the plasma may be implanted into the donorsubstrate, leading to undesired doping and even damage of the film to beseparated.

Ion shower is also mentioned in U.S. Pat. No. 6,027,988 as anon-mass-separated ion implantation method, the relevant portion thereofis incorporated herein by reference. However, this reference does nothave detailed description of ion shower, nor does it provide anyconcrete example of using ion shower for ion implantation. Ion showerimplantation (ISI) uses a large area ion beam derived from a plasmasource by using, for example, an extraction electrode. The ions may beaccelerated before implantation. Typical use of ion shower for ionimplantation is described, for example, in F. Kröner et al., PhosphorusIon Shower Implantation for Special Power IC Applications, IonImplantation Technology (2000), 476-79, the relevant portion thereof isincorporated herein by reference. FIG. 3 schematically illustrates theuse of a conventional ion shower for ion implantation. In the equipment301, there are two separate chambers: a plasma chamber 307 containing aplasma 309 between electrode 303 and electrode grid 305; and animplantation chamber 313 in which a wafer 315 is placed. The ions 311,optionally further accelerated, travel and partly enter into wafer 315.Thus clearly, the conventional ion shower has the followingcharacteristics: (i) the use of a remote plasma generated in a separateplasma chamber; (ii) the wafer for implantation is not placed in anelectric field; and (iii) unlike PIII, the ion source is continuous butnot pulsed; and (iv) the ions are not mass-separated, thus the ions thatimpinge on the wafer to be implanted actually contain a plurality ofspecies with various mass, charges and energy.

Ion shower has been used in the implantation of large ions, such asphosphorous and the like, into semiconductor materials, for the purposessuch as doping. However, it is unclear to the present inventors from theprior art whether it can be used successfully for splitting a thin filmfrom a donor semiconductor wafer due to the scant disclosure thereof inreferences such as U.S. Pat. No. 6,027,988. Moreover, the presentinventors have discovered that replacing the beam line ion implantationequipment and process used in the prior art in the manufacture ofsemiconductor devices such as integrated circuits with ion shower is notas simple and easy as it seems. Substantial technical challenges wereencountered.

As described infra, the present inventors have discovered that, by usingnon-mass-separated ion shower, damage to the crystalline structure ofthe exfoliation film can be caused. The damage can be so severe thatthey cannot be used for the manufacture of a lot of microelectronicstructures, such as the circuit features of integrated circuits, thusare highly undesirable.

Without intending to be bound by any particular theory, the presentinventors believe that the damage to the crystalline structure of theexfoliation film is caused by impurities in the conventional ion shower.In the ion beam of a conventional ion shower, in the plasma chamber, aplurality of ions having differing mass and charges are simultaneouslygenerated, and allowed to impinge on the donor substrate and implantedtherein. For example, where hydrogen ion shower is used, in the hydrogenplasma, a plurality of ions belong to differing species, such as H⁺, H₂⁺ and H₃ ⁺ are produced at various proportions. Due to different sizesand mass, these ions travel at different distances in the donorsubstrate. Some of them would not reach the ion implantation zone butare implanted in the exfoliation film, causing undesired modificationand damage. Moreover, the plasma may further comprise ions such as P+,B+, oxygen ions, carbon ions, fluorine ions and chlorine ions and metalsions due to contamination of the plasma chamber. These large and heavyions would more than likely retain in the exfoliation film and causedamage.

Therefore, the present inventors made the present invention to solve theassociated problems of the prior art methods such as PIII and beam lineion implantation, as well as the drawback of conventional ion showerimplantation.

The first aspect of the present invention is thus a process for makingSOI structures at large comprising the following steps:

(I) providing a donor substrate comprising semiconductor material havinga first donor external surface; and

(II) implanting a plurality of ions belonging to a first species throughthe first donor external surface into an ion implantation zone at adepth below the first donor external surface by using a first ion showerpurified by electromagnetic separation such that the structure of atleast a 50 nm part, in certain embodiments at least a 100 nm thick part,in certain embodiments at least a 150 nm part, in certain embodiments atleast a 200 nm thick part, of the film of material sandwiched betweenthe ion implantation zone and the first donor external surface(“exfoliation film”) is essentially not damaged.

As mentioned above, in step (I), the donor substrate may be comprised ofany semiconductor material, such as the silicon-based semiconductormaterials and non-silicon-based semiconductor materials. Thesemiconductor material may be essentially pure and single-crystalline,or be previously doped with desired dopants to modify the structure andelectric conductivity thereof. In the current semiconductor industry,the most widely used donor substrate is based on single-crystallinesilicon, and the most widely produced structure is SiOI structures, suchas silicon on oxidized silicon wafers. The present invention can beadvantageously applied to such processes to reduce the cost thereof.

In typical semiconductor processes, the donor substrate used haveprecision polished, highly flat and smooth surfaces. In many situations,the donor substrates are wafers having essentially parallel majorsurfaces. The present invention may be applied in those situations.However, it is also understood that the donor substrate may have acontoured surface, or even more than one contoured surfaces depending onthe surface topography of a recipient substrate to receive theexfoliation film or the intended use of the SOI structure to beproduced. It is also possible that the donor substrate has externalsurfaces characterized by grooves and other features. The use ofpurified ion-shower according to the process of the present inventionmay be applied to those donor substrates.

One of ordinary skill in the art knows the desired depth of the ionimplantation zone in the donor substrate according to the intended useof the SOI structure and in light of the teachings of the presentapplication. The depth of the ion implantation zone below the firstdonor external surface determines the thickness of the exfoliation film.Typically, for the purpose of producing a exfoliation film from thedonor substrate, the depth of the ion implantation zone is less thanabout 1000 nm, in certain embodiments less than about 500 nm, in certainembodiments less than about 300 nm, in certain embodiments less thanabout 150 nm, in certain embodiments less than about 100 nm. Generally,using ion shower, especially the mass-separated ion shower according tothe present invention can result in shallower depth of the ionimplantation zone, thus a thinner exfoliation film, than using the beamline ion implantation of the prior art, thus reducing down-streamthinning of the exfoliation film. By varying the kinetic energy of theimplanting ions, one can change the depth of the ion implantation zone.For example, when implanting single-crystalline silicon donor substrateswith H₃ ⁺ ions, the energy of the ions may be chosen within the range ofabout 40 to 70 KeV to obtain a desired thickness of the exfoliationfilm.

As mentioned supra, in order for the ions to be implanted into the ionimplantation zone, it is highly desired that the ions comprised in theion shower are pure. Thus, the ions belonging to a first species, suchas H⁺, H₂ ⁺, H₃ ⁺, He⁺, He²⁺, and the like, desirably have a purity of aat least 90% by mole, in certain embodiments at least 95% by mole, incertain embodiments at least 99% by mole, in certain embodimentspreferably at least 99.5%, in certain embodiments preferably at least99.9%, in certain embodiments at least 99.99%.

It is known that ions with differing mass and charges can be separatedby allowing them to travel through an intersecting electric and/ormagnetic field. The travel paths of the ions will be altered by theLorentz force to different degrees depending on their respective massand charges according to the following equation:

=q(

+

×

)where

is the Lorentz force vector;

is the electric field intensity vector;

is the instantaneous velocity vector;

is the magnetic field intensity vector; and q is the electric charge ofthe ion. Thus the Lorentz force has two split elements: the electricforce element, and the magnetic force element. The magnetic force isperpendicular to the direction of vector

according to the right-hand rule. One skilled in the art, in the lightof the disclosure herein, will be able to determine the desired magneticfield

used in isolating the individual ion species produced in the ion shower,selecting the desired ones and directing them to the surface of thedonor substrate, and filtering out or directing away the undesired andcontaminant ions.

FIG. 4 schematically illustrates the apparatus set-up for the process ofthe present invention. Thus, compared to FIG. 3 which schematicallyillustrates the conventional ion shower, a magnetic analyzer 403 isplaced in between the plasma chamber 307 and the implantation chamber313. A magnetic field 405 is applied in the analyzer 403, whichseparates the different species of ions according to their respectivemass and charges. The thus purified ions of the desired species aredirected into the implantation chamber and used for implantationpurpose.

In general, when ion showers are used as the ion sources, includingconventional ion showers and the mass-separated ion showers according tothe present invention, the donor substrate to be ion-implanted is notplaced in an electric field. However, in certain situations, it may bedesired that that the ions, upon exiting the grid electrode, or uponseparation in the electromagnetic analyzer, may need to be acceleratedor decelerated so that the ions have the desired energy levels forimplanting into the depth. This can be achieved by subjecting to theions to additional accelerating/decelerating electric field. The donorsubstrate may be placed inside or outside of theaccelerating/decelerating electric field.

Thus, the process according to the first aspect enables ion implantationwith high purity ions essentially free of damaging species and having anarrow range of energy levels. This, in turn, enables the precisecontrol of the depth and thickness of the ion implantation zone, whichis highly desirable in the manufacture of SOI structures.

FIG. 1 illustrates schematically an embodiment of a donor substrate 101implanted by using process of the present invention involvingmass-separated ion shower according to the present invention. 103 is thefirst donor external surface, 105 is the second donor external surface,and 113 is the ion implantation zone in which a plurality of ions, suchas H₃ ⁺ or He⁺ are implanted. The film of material 115 sandwichedbetween the ion implantation zone 113 and the first donor externalsurface 103 is the exfoliation film. 109 in this figure represents thezone immediately below the in implantation zone 113. The ionimplantation zone 113 has a thickness of t, and a depth under the firstdonor external surface of t_(f). The t_(f) is also the thickness of theintended exfoliation film 115.

As discussed supra, in a single ion implantation operation, multiplespecies of ions present in the ion beam is generally undesirable.However, ion implantation using multiple ions may be desirable in themanufacture of certain SOI structures. The present inventors havediscovered that, in the manufacture of certain SOG structures, ionimplantation using multiple ion species may actually lower the totalamount of implanted ions needed to achieve the desired exfoliation andenhance the efficiency of the overall implantation process. According tothe present invention, such implantation of multiple ion species can beachieved by, e.g., upon completion of implanting a first species of ionsinto the ion implantation zone, implementing a second step of ionimplantation as follows:

(III) implanting a plurality of ions belonging to a second speciesthrough the first donor external surface into the ion implantation zoneat the depth below the first donor external surface by using a secondion shower purified by electromagnetic separation such that thestructure of the exfoliation film of material is essentially notdamaged, said ions belonging to the second species being different fromthe ions belonging to the first species.

The first ion implantation zone and second ion implantation zone maydiffer slightly within the donor substrate. However, due to thecontrollability of the process of the present invention as discussedsupra, one skilled in the art in the light of teachings of the presentapplication can choose the proper process parameters such that both ofthem are located within the ion implantation zone. Indeed, both of themcan be controlled such that they substantially overlap. Generally, it isdesired that D_(p)≦300 nm, where D_(p) is the distance between the peakof the ions belonging to the first species in the first ion implantationzone and the peak of the ions belonging to the second species in thesecond ion implantation zone, in the donor substrate. In certainembodiments it is preferred that D_(p)≦200 nm, in certain otherembodiments, D_(p)≦100 nm. In certain embodiments, D_(p)≦50 nm.

FIG. 2 schematically illustrates an implanted donor substrate 201ion-implanted with two species of ions. In the overall ion implantationzone 113, there are two substantially overlapping zones: the first ionimplantation zone 111 and the second ion implantation zone 115. In aparticular embodiment of the process according to the first aspect ofthe present invention, H₃ ⁺ and He⁺ are used as the first and secondspecies of ions for implantation, or vice versa. The order of implantingH₃ ⁺ or He⁺ first or second is not critical, though in certainembodiments it is desired that H₃ ⁺ ions are implanted first. Thiscombination of H₃ ⁺ and He⁺ according to the present invention isparticularly useful and advantageous for implanting and exfoliating asilicon donor substrate. When implanting single-crystalline siliconsubstrate, to reach the same ion implantation zone for both H₃ ⁺ andHe⁺, the energy needed for the He⁺ is smaller. The present inventorshave discovered that by using (i) ion implantation of H₃ ⁺ ions only or(ii) a combination of H₃ ⁺ and He⁺ ion implantation, exfoliation ofsilicon film can be successfully achieved. However, due to the lowertotal energy and higher efficiency of (ii), it is preferred over (i). Inone particular embodiment of (ii), the energy of H₂ ⁺ ions was about 70KeV, and the energy of He⁺ was about 40 KeV, which resulted in excellentexfoliation of silicon film.

As discussed above, at least a part of a 50 nm thick, in certainembodiments at least a part of 100 nm thick, in certain embodiments atleast a part of 150 nm thick, in certain embodiments at least a part of200 nm thick, of the exfoliation film produced by using the processaccording to the present invention is not damaged by theion-implantation process. In is preferred that the structure of at leasta majority of the thickness of the exfoliation film is not damaged. By“majority”, it is meant at least half of the thickness of theexfoliation film is not damaged. By “not damaged,” it is meant that theinternal structure of the film, or the non-damaged part thereof, is notsignificantly altered during the ion-implantation process, such that theexfoliation film, or the relevant part thereof, may not be suitable foruse in the intended applications.

The thickness of the ion implantation zone, comprising a singleimplanted ion species or multiple implanted ion species, can becontrolled to be less than about 1000 nm, in certain embodiments lessthan about 500 nm, in certain other embodiments less than about 300 nm,in certain other embodiments less than about 200 nm, according to theprocess of the present invention.

Upon ion implantation, the exfoliation film may be separated from therest of the donor wafer by using methods described, e.g., in US2004/0229444. Without intending to be bound by any particular theory, itis believed that the ions implanted causes defects in the implantationzone upon further treatment, such as heating, by, e.g., forming microgas bubbles. The high density of defects in that zone leads to thesplitting at a location within the implantation zone and exfoliation ofthe exfoliation film and part of the implantation zone from the rest ofthe donor substrate.

A substantially independent exfoliation film may be produced bysplitting the exfoliation film from the donor substrate upon ionimplantation in a step (V):

separating the exfoliation film and at least part of the material in theion implantation zone from the donor substrate at a location within theimplantation zone.

The thin film may then be used for down stream processing in themanufacture of SOI structures, such as by bonding to an insulatorrecipient substrate afterwards. However, because the exfoliation film isvery thin, it is usually very difficult to handle without a pre-bondedsupport. Thus, typically, in the process for making SOI structuresaccording to the first aspect of the present invention, prior toseparation of the exfoliation film in step (V), the following step (IV)is implemented:

(IV) bonding the first donor external surface to a recipient substrate.

The recipient substrate for bonding to the donor substrate can be asemiconductor wafer with or without an oxide surface layer; a glassplate; a plate of crystalline materials, and a glass-ceramic plate. Incertain embodiments, the recipient substrate is a single-crystallinesilicon wafer with a surface oxidation layer formed by, e.g., thermalgrowth of SiO₂ layer, and the like. In certain embodiments, therecipient substrate comprises SiO₂. In certain embodiments, therecipient substrate is a high-purity SiO₂ plate. In certain embodiments,the recipient substrate comprises a crystalline material such assapphire. In certain embodiments, the recipient substrate comprises anoxide glass or oxide glass-ceramic material. As is described in US2004/0229444 A1, in certain embodiments, the recipient substratecomprises an oxide glass or oxide glass-ceramic materials having metalions. Thus, the process according to the first aspect of the presentinvention may be advantageously used for the production of (i)conventional SOI and SiOI structures where in the past beam line ionimplantation has been used, and (ii) un-convention SOI structures, suchas SOG and SiOG structures described in US 2004/0229444 A1.

Conventional bonding methods used in the semiconductor industry, such aswafer bonding, fusion bonding, and anodic bonding.

A method particularly useful in bonding the donor substrate to a glassor glass-ceramic recipient substrate, illustrated in US 2004/0229444 A1,involves applying (a) forces to the donor and recipient substrates suchthat they are pressed into close contact; (b) electric field within thedonor and recipient substrates such that the electrical potential in thedonor substrate is higher than that in the recipient substrate; and (c)a temperature gradient between the donor and recipient substrates.

After ion implantation of the donor substrate, but before bonding thedonor substrate to the recipient substrate, surface cleaning of bothsubstrates are usually required in order to obtain bonding withsufficient strength. For example, after hydrogen ion implantation to asilicon substrate, a plurality of hydrogen groups are generated at thesurface of the exfoliation film. Directly bonding the exfoliation filmsurface to a surface of the recipient substrate without reducing oreliminating the surface hydrogen groups usually requires the use ofsignificantly higher external force due to the repulsion caused by thesurface groups. Thus, a step is usually needed after the ionimplantation but before bonding to reduce the hydrogen groups from thesurface. As is taught in US 2004/0229444 A1, such hydrogen groupreduction can be effected by, inter alia, oxygen plasma treatment, ozonetreatment, H₂O₂ treatment, H₂O₂ and ammonia treatment, and H₂O₂ and acidtreatment.

The second aspect of the present invention is directed to a process formaking SOG structure by using mass-separated ion shower. In broad terms,it comprises the following steps:

(A1) providing a donor substrate and a recipient substrate, wherein:

(1) the donor substrate comprises a semiconductor material and a firstdonor external surface for bonding with the recipient substrate (firstbonding surface) and a second donor external surface;

(2) the recipient substrate comprises an oxide glass or oxideglass-ceramic and two external surfaces: (i) a first recipient externalsurface for bonding to the first substrate (the second bonding surface);and (ii) a second recipient external surface;

(A2) implanting a plurality of ions belonging to a first species throughthe first donor external surface into an ion implantation zone of thedonor substrate at a depth below the first donor external surface byusing a first ion shower purified by electromagnetic separation suchthat the internal structure of at least a part 50 nm thick, in certainembodiments at least a part 100 nm thick, in certain embodiments atleast a part 150 nm thick, in certain embodiments at least a part 200 nmthick, of the film of material sandwiched between the ion implantationzone and the first donor external surface (“exfoliation film”) isessentially not damaged;

(B) after steps (A1) and (A2), bringing the first and second bondingsurfaces into contact;

(C) for a period of time sufficient for the donor and recipientsubstrates to bond to one another at the first and second bondingsurfaces, simultaneously:

(1) applying forces to the donor substrate and/or the recipientsubstrate such that the first and second bonding surfaces are pressedinto contact;

(2) subjecting the donor and recipient substrates to an electric fieldhaving a general direction of from the second recipient external surfaceto the second donor external surface; and

(3) heating the donor and recipient substrates, said heating beingcharacterized in that the second donor and recipient external surfaceshave average temperatures T₁, and T₂, respectively, said temperaturesbeing selected such that upon cooling to a common temperature, the donorand recipient substrates undergo differential contraction to therebyweaken the donor substrate at the ion implantation zone; and

(D) cooling the bonded donor and recipient substrates and splitting thedonor substrate at the ion implantation zone;

wherein the oxide glass or oxide glass-ceramic comprises positive ionswhich during step (C) move within the recipient substrate in a directionaway from the second bonding surface and towards the second recipientexternal surface.

Thus the second aspect is an embodiment of the first aspect of thepresent invention described supra in general terms. Thus, the firstaspect of the present invention is further illustrated by the followingdescription of the second aspect. The above generally description of thefirst aspect of the present invention is also applicable to the secondaspect mutatis mutandis.

FIGS. 5 and 6 schematically illustrate an embodiment of the processaccording to the second aspect of the present invention. In FIG. 5, asemiconductor donor substrate 101 shown in FIG. 1 is allowed to bondwith a glass or glass-ceramic recipient substrate 501 having a firstrecipient external surface 503 (second boding surface) and a secondrecipient external surface 505. A pressure P is applied so that thefirst donor external surface 103 (first bonding surface) and the firstrecipient external surface 503 (second bonding surface) are placed intoclose contact. The donor substrate 101 is heated to a temperature T₁ andapplied with a voltage V₁. The recipient substrate 501 is heated to adiffering temperature T₂ and applied with a lower voltage V₂. Thusbonding between the donor substrate 101 and the recipient substrate 501is effected by applying external pressure, temperature gradient andelectric field. After bonding for a sufficient period of time, thevoltages and pressure applied to the substrates are withdrawn, and thesubstrates were allowed to cool to a common temperature T₃ (such as roomtemperature). Due to differential contraction of both substrates(explained in more details infra), the ion implantation zone 113 isweakened and separated into two parts: 113 a bonding to the exfoliationfilm 115 which is bonded to the recipient substrate, and 113 b bondingto the rest of the donor substrate.

Certain specific embodiments of the process according to the secondaspect of the present invention may comprise the following steps:

-   -   (A′) providing first and second substrates wherein:        -   (1) the first substrate comprises a first external surface            for bonding to the second substrate (the first bonding            surface), a second external surface for applying force to            the first substrate (the first force-applying surface), and            an internal zone for separating the first substrate into a            first part and a second part (the internal zone is            hereinafter referred to as the “separation zone,” which, is            an ion implantation zone formed by using the purified ion            shower implantation according to the first aspect of the            present invention, described supra), wherein:            -   (a′) the first bonding surface, the first force-applying                surface, and the separation zone are substantially                parallel to one another;            -   (b′) the second part is between the separation zone and                the first bonding surface; and            -   (c′) the first substrate comprises a substantially                single-crystalline semiconductor material; and        -   (2) the second substrate comprises two external surfaces,            one for bonding to the first substrate (the second bonding            surface) and another for applying force to the second            substrate (the second force-applying surface), wherein:            -   (a′) the second bonding surface and the second                force-applying surface are substantially parallel to one                another and are separated from one another by a distance                D₂; and            -   (b′) the second substrate comprises an oxide glass or an                oxide glass-ceramic;    -   (B′) bringing the first and second bonding surfaces into contact        (once brought into contact, the first and second bonding        surfaces form what is referred to herein as the “interface”        between the first and second substrates);    -   (C′) for a period of time sufficient for the first and second        substrates to bond to one another at the first and second        bonding surfaces (i.e., at the interface), simultaneously:        -   (1) applying force to the first and second force-applying            surfaces to press the first and second bonding surfaces            together;        -   (2) subjecting the first and second substrates to an            electric field which is characterized by first and second            voltages V₁ and V₂ at the first and second force-applying            surfaces, respectively, said voltages being uniform at those            surfaces with V₁ being higher than V₂ so that the electric            field is directed from the first substrate to the second            substrate; and        -   (3) heating the first and second substrates, said heating            being characterized by first and second temperatures T₁ and            T₂ at the first and second force-applying surfaces,            respectively, said temperatures being uniform at those            surfaces and being selected so that upon cooling to a common            temperature, the first and second substrates undergo            differential contraction to thereby weaken the first            substrate at the separation zone; and    -   (D′) cooling the bonded first and second substrates (e.g., to a        common temperature such as room temperature) and separating the        first and second parts at the separation zone;        wherein the oxide glass or oxide glass-ceramic has one or both        of the following sets of characteristics:

(i) the oxide glass or oxide glass-ceramic has a strain point of lessthan 1,000° C. and comprises positive ions (e.g., alkali oralkaline-earth ions) which during step (C′), move within the secondsubstrate in a direction away from the second bonding surface andtowards the second force-applying surface; and/or

(ii) the oxide glass or oxide glass-ceramic comprises (a′) non-bridgingoxygens and (b′) positive ions (e.g., alkali or alkaline-earth ions)which during step (C′), move within the second substrate in a directionaway from the second bonding surface and towards the secondforce-applying surface.

As known in the art, non-bridging oxygens in an oxide glass or in theglass phase of an oxide glass-ceramic are those oxygens contributed tothe glass by non-network forming components of the glass. For example,in the case of commercially available LCD display glass such as CorningIncorporated Glass No. 1737 and Corning Incorporated Glass No. EAGLE2000™, the non-bridging oxygens include those oxygens which are part ofthe glass through the incorporation of alkaline-earth oxides (e.g., MgO,CaO, SrO, and/or BaO) in the glass composition.

Although not wishing to be bound by any particular theory of operation,it is believed that an electrolysis-type reaction takes place duringstep (C′). In particular, it is believed that the semiconductorsubstrate (first substrate) serves as the positive electrode for theelectrolysis-type reaction and that reactive oxygen is produced in theregion of the interface between the first and second substrates. Thisoxygen is believed to react with the semiconductor material (e.g.,silicon) forming, in situ, a hybrid region of oxidized semiconductor(e.g., a silicon oxide region for a silicon-based semiconductor). Thishybrid region begins at the interface and extends into the firstsubstrate. The presence of non-bridging oxygens in the oxide glass oroxide glass-ceramic of the second substrate is believed to play a rolein the generation of the oxygens that react with the semiconductormaterial of the first substrate.

It is believed that such generation of reactive oxygen and itscombination with the semiconductor material is a source of the strongbond between the semiconductor material of the first substrate and theoxide glass or oxide glass-ceramic of the second substrate, i.e., atleast a part (and potentially all) of the bond between the first andsecond substrates is through the reaction of the semiconductor materialwith reactive oxygen originating from the second substrate.Significantly, unlike prior techniques, this strong bond is achievedwithout the need for a high temperature treatment, i.e., a treatment ata temperature above 1,000° C.

This ability to avoid high temperature processing allows the secondsubstrate to be a material which can be manufactured in large quantitiesat low cost. That is, by eliminating high temperature processing, theinvention eliminates the need for a support substrate composed of anexpensive high temperature material, such as, silicon, quartz, diamond,sapphire, etc.

In particular, the ability to achieve a strong bond without the need fora high temperature treatment allows the second substrate to be composedof an oxide glass or an oxide glass-ceramic in one embodiment the glassor glass-ceramic exhibits a strain point less than 1,000° C. Moreparticularly, for display applications, the oxide glass or oxideglass-ceramic typically has a strain point less than 800° C., and infurther embodiments less than 700° C. For electronics and otherapplications, the strain point is preferably less than 1,000° C. As wellknown in the glass making art, glasses and glass-ceramics having lowerstrain points are easier to manufacture than glasses and glass-ceramicshaving higher strain points.

To facilitate bonding, the oxide glass or oxide glass-ceramic should beable to conduct electricity at least to some extent. The conductivity ofoxide glasses and oxide glass-ceramics depends on their temperature andthus in achieving a strong bond between the semiconductor material andthe oxide glass or oxide glass-ceramic, there is a balance among: 1) theconductivity of the glass or glass-ceramic, 2) the temperatures (T₁ andT₂) used in step (C′), 3) the strength of the electric field applied tothe first and second substrates during step (C′), and 4) the amount oftime during which step (C′) is performed.

As a general guideline, the oxide glass or oxide glass-ceramicpreferably has a resistivity ρ at 250° C. that is less than or equal to10¹⁶ Ω·cm (i.e., a conductivity at 250° C. that is greater than or equalto 10⁻¹⁶ Siemens/cm). More preferably, ρ at 250° C. is less than orequal to 10¹³ Ω·cm, and most preferably, it is less than or equal to10^(11.5) Ω·cm. It should be noted that although quartz has therequisite resistivity at 250° C. of 10^(11.8) Ω·cm, it lacks positiveions that can move during step (C′), and it thus follows that quartz isunsuitable for use as the second substrate in producing SOI structuresin accordance with the above procedures.

For any particular set of first and second substrates, persons skilledin the art will readily be able to determine suitable combinations oftime, temperature, and field strength for step (C′) from the presentdisclosure. In particular, such persons will be able to selectcombinations of these parameters which create a bond between thesemiconductor and the oxide glass or oxide glass-ceramic which is strongenough for the SOI structure to withstand the various forces andenvironmental conditions to which it will be exposed during furtherprocessing and/or use.

In addition to the above role in bonding, the electric field applied instep (C′) also moves positive ions (cations) within the second substratein a direction from the second substrate's bonding surface (the secondbonding surface) towards its force-applying surface (the secondforce-applying surface). Such movement preferably forms a depletionregion (23) which begins at the interface between the first and secondsubstrates and extends into the second substrate, i.e., the depletionregion begins at the second bonding surface and extends into the secondsubstrate towards the second force-applying surface.

The formation of such a depletion region is especially desirable whenthe oxide glass or oxide glass-ceramic contains alkali ions, e.g., Li⁺¹,Na⁻¹, and/or K⁺¹ ions, since such ions are known to interfere with theoperation of semiconductor devices. Alkaline-earth ions, e.g., Mg⁺²,Ca⁺², Sr⁺², and/or Ba⁺², can also interfere with the operation ofsemiconductor devices and thus the depletion region also preferably hasreduced concentrations of these ions.

Significantly, it has been found that the depletion region once formedis stable over time even if the SOI structure is heated to an elevatedtemperature comparable to, or even to some extent higher than, that usedin step (C′). Having been formed at an elevated temperature, thedepletion region is especially stable at the normal operating andformation temperatures of SOI structures. These considerations ensurethat alkali and alkaline-earth ions will not diffuse back from the oxideglass or oxide glass-ceramic into the semiconductor of the SOI structureduring use or further device processing, which is an important benefitderived from using an electric field as part of the bonding process ofstep (C′).

As with selecting the operating parameters to achieve a strong bond, theoperating parameters needed to achieve a depletion region of a desiredwidth and a desired reduced positive ion concentration for all of thepositive ions of concern can be readily determined by persons skilled inthe art from the present disclosure. When present, the depletion regionis a characteristic feature of an SOI structure produced in accordancewith the method aspects of the present invention.

In addition to the depletion region, the application of the electricfield can also create “pile-up” regions for one or more of the mobilepositive ions contained in the oxide glass or oxide glass-ceramic. Whenpresent, such regions are located at or near the side (edge) of thedepletion region farthest from the interface between the first andsecond substrates. Within the pile-up region, the positive ion has aconcentration above its bulk concentration. For example, when measuredin atomic percent, the peak concentration of the positive ion in thepile-up region can be, for example, up to 5 times greater than the bulkconcentration. Like the depletion region, such a pile-up region, whenpresent, is a characteristic feature of an SOI structure produced inaccordance with the second aspect of the present invention.

The temperatures of the first and second substrates during step (C′),i.e., the values of T₁, and T₂, are chosen to perform the importantfunction of weakening (e.g., fracturing) the semiconductor substrate(first substrate) at the separation zone so that the first substrate canbe divided into first and second parts, the second part being bonded tothe second substrate. In this way, an SOI structure having asemiconductor portion of a desired thickness is achieved, e.g., athickness Ds between, for example, 10 nanometers and 500 nanometers and,in some cases, up to 5 microns.

Although not wishing to be bound by any particular theory of operation,it is believed that the weakening of the semiconductor substrate at theseparation zone primarily occurs as the bonded first and secondsubstrates are cooled after step (C′), e.g., to room temperature. By theproper selection of T₁, and T₂ (see below), this cooling causes thefirst and second substrates to differentially contract. Thisdifferential contraction applies stress to the first substrate whichmanifests itself as a weakening/fracturing of the first substrate at theseparation zone. As discussed below, preferably, the differentialcontraction is such that the second substrate seeks to contract morethan the first substrate.

As used herein, the phrase “differential contraction upon cooling to acommon temperature” and similar phrases mean that if the first andsecond substrates were not bonded, they would contract to differentextents by such cooling. However, since the first and second substratesbecome bonded during step (C′) and are rigid materials, the amount ofcontraction of the individual substrates which actually occurs will bedifferent from that which would occur if there were no bonding. Thisdifference leads to one of the substrates experiencing tension and theother compression as a result of the cooling. The phrase “seeks tocontract” and similar phrases are used herein to reflect the fact thatthe contraction of the substrates when bonded will in general bedifferent from their non-bonded contraction, e.g., the substrate beingdiscussed may seek to contract to a certain extent as a result of thecooling but may not and, in general, will not actually contract to thatextent as a result of being bonded to the other substrate.

The values of T₁, and T₂ used during step (C′) will depend on therelative coefficients of thermal expansion of the first and secondsubstrates, the goal in choosing these values being to ensure that oneof the substrates, preferably, the second substrate, seeks to contractto a greater extent than the other substrate, preferably, the firstsubstrate, so as to apply stress to, and thus weaken, the separationzone during cooling.

In general terms, in order for the second substrate to seek to contractto a greater extent than the first substrate during cooling, T₁, T₂, andthe CTE's of the first and second substrates (CTE₁ and CTE₂,respectively) should satisfy the relationship:CTE₂ ·T ₂>CTE₁ ·T ₁,

where CTE₁ is the 0° C. coefficient of thermal expansion of thesubstantially single-crystalline semiconductor material and CTE₂ is the0-300° C. coefficient of thermal expansion of the oxide glass or oxideglass-ceramic. This relationship assumes that the first and secondsubstrates are cooled to a common reference temperature of 0° C., and T₁and T₂ are expressed in terms of ° C.

In applying this relationship, it should be kept in mind that the oxideglass or oxide glass-ceramic preferably has a 0-300° C. coefficient ofthermal expansion CTE which satisfies the relationship:5×10⁻⁷/° C.≦CTE≦75×10⁻⁷/° C.

For comparison, the 0° C. coefficient of thermal expansion ofsubstantially single-crystalline silicon is approximately 24×10⁻⁷/° C.,while the 0-300° C. average CTE is approximately 32.3×10⁻⁷/° C. Althougha CTE for the second substrate which is less than or equal to 75×10⁻⁷/°C. is generally preferred, in some cases, the CTE of the secondsubstrate can be above 75×10⁻⁷/° C., e.g., in the case of soda limeglasses for use in such applications as solar cells.

As can be seen from the CTE₂·T₂>CTE₁·T₁ relationship, when the CTE ofthe oxide glass or oxide glass-ceramic (CTE₂) is less than that of thesemiconductor material (CTE₁), a larger T₂-T₁ difference will be neededin order for the second substrate to seek to contract more than thefirst substrate during cooling. Conversely, if the CTE of the oxideglass or oxide glass-ceramic is greater than that of the semiconductormaterial, a smaller T₂-T₁ difference can be used. Indeed, if the CTE ofthe oxide glass or oxide glass-ceramic is sufficiently above than thatof the semiconductor material, the T₂-T₁ difference can become zero oreven negative. However, in general, the CTE of the oxide glass or oxideglass-ceramic is chosen to be relatively close to that of thesemiconductor material so that a positive T₂-T₁ difference is needed toensure that the second substrate will seek to contract more than thefirst substrate during cooling. Having T₂>T₁ is also desirable since itcan aid in bonding of the oxide glass or oxide glass-ceramic to thesemiconductor material since it tends to make the oxide glass or oxideglass-ceramic more reactive. Also, having T₂>T₁ is desirable since itcan facilitate movement of positive ions away from the interface betweenthe first and second substrates.

The differential contraction between the first and second substratesduring cooling and the resulting weakening/fracturing of the firstsubstrate at the separation zone can be achieved by approaches otherthan having the second substrate seek to contract more than the firstsubstrate during the cooling. In particular, it can be the firstsubstrate that seeks to contract more than the second substrate. Again,this differential contraction is achieved through the selection of theCTE's and temperatures of the first and second substrates. In generalterms, for this case, CTE₁·T₁ needs to be greater than CTE₂·T₂.

When the first substrate seeks to contract more than the secondsubstrate, the first substrate and, in particular, the second part ofthe first substrate, will end up under tension, rather than undercompression, at the end of the cooling. In general, it is preferred forthe semiconductor film (second part of the first substrate) to be undercompression in the finished SOI structure, which makes the approach inwhich the differential contraction causes the second substrate to seekto contract more than the first substrate during cooling preferred. Forsome applications, however, having the semiconductor film under sometension may be preferred.

Thus, to summarize, although other sets of conditions can be used in thepractice of the invention, in the preferred embodiments of theinvention, T₂ is greater than T₁ during step (C′) and the secondsubstrate seeks to contract more than the first substrate during coolingfrom the elevated temperatures used during step (C′).

Again, for any particular application of the invention (e.g., anyparticular semiconductor material and any particular oxide glass oroxide glass-ceramic), persons skilled in the art will readily be able toselect values for T₁ and T₂ based on the present disclosure and thedisclosure of US 2004/0229444A which should provide a level ofdifferential contraction sufficient to weaken the separation zone sothat the first and second parts of the first substrate can be separatedfrom one another to produce the desired SOI structure.

Separation of the first and second parts at the separation zone resultsin each part having an “exfoliation” surface where the separationoccurred. As known in the art, upon initial formation, i.e., before anysubsequent surface treatments, such an exfoliation surface ischaracterized by a surface roughness which is generally at least on theorder of less than 1 nanometers RMS, e.g., in the range of 1-100nanometers, and depending on the process conditions used, will typicallyhave a concentration of the implanted ion used to form the separationzone, e.g., hydrogen, helium, and the like, above that present in thebody of the first or second parts. In typical applications, theexfoliation surface is polished prior to use so that its RMS surfaceroughness is reduced to 1 nanometer or less, e.g., to a RMS surfaceroughness on the order of 0.1 nanometers for electronic applications. Asused herein, the phrase “exfoliation surface” includes the surface asinitially formed and the surface after any subsequent treatments.

The pressure applied to the first and second substrates during step (C′)ensures that those substrates are in intimate contact while undergoingthe heat and electric field treatments of that step. In this way, strongbonding between the substrates can be achieved.

Generally, the semiconductor substrate (the first substrate, also thedonor substrate) will be able to withstand higher levels of appliedpressure than the glass or glass-ceramic substrate (the secondsubstrate). Thus, the pressure is chosen to provide intimate contactbetween the substrates without damaging the second substrate.

A wide range of pressures can be used. For example, the force per unitarea P′ applied to the first and second force-applying surfaces of thefirst and second substrates, respectively, preferably satisfies therelationship:1 psi≦P′≦100 psi;and most preferably, the relationship:1 psi≦P′≦50 psi.

Again, the specific pressure value to be used for any particularapplication of the invention can be readily determined by personsskilled in the art from the present disclosure.

The second aspect of the invention can be practiced using a single firstsubstrate and a single second substrate. Alternatively, the methods ofthe invention can be used to form more than one SOI structure on asingle second substrate.

For example, steps (A′) through (D′) can be used to form a first SOIstructure which does not cover the entire area of the second substrate.Thereafter, steps (A′) through (D′) can be repeated to form a second SOIstructure which covers all or part of the area not covered by the firstSOI structure. The second SOI structure may be the same or differentfrom the first SOI structure, e.g., the second SOI structure can be madeusing a first substrate composed of a substantially single-crystallinesemiconductor material that is the same or different from thesemiconductor material of the first substrate used in producing thefirst SOI structure.

More preferably, multiple SOI structures are formed simultaneously on asingle second substrate by providing multiple (i.e., two or more) firstsubstrates in step (A′), bringing all of those first substrates intocontact with a single second substrate in step (B′), and then performingsteps (C′) and (D′) on the resulting multiple first substrate/singlesecond substrate assembly. The multiple first substrates provided instep (A′) can all be the same, all different, or some the same and somedifferent.

Whichever approach is used, the resulting multiple SOI structures on asingle oxide glass or oxide glass-ceramic substrate can be contiguous orseparated as appropriate for the particular application of theinvention. If desired, gaps between some or all of the adjacentstructures can be filled with, for example, semiconductor material toobtain one or more continuous semiconductor layers on an oxide glass oroxide glass-ceramic substrate of any desired size.

The SOI structures produced according to the second aspect of thepresent invention is desirably a semiconductor-on-insulator structurecomprising first and second layers which are attached to one anothereither directly or through one or more intermediate layers, wherein:

(a′) the first layer comprises a substantially single-crystallinesemiconductor material;

(b′) the second layer comprises an oxide glass or an oxideglass-ceramic; and

(c′) the bond strength between the first and second layers is at least 8joules/meter², preferably at least 10 joules/meter², and most preferablyat least 15 joules/meter².

As used throughout this specification and in the claims, the bondstrength between a semiconductor layer and a glass or glass-ceramiclayer of an SOI structure is determined using an indentation procedure.Such procedures are widely used to assess the adhesion characteristicsof thin films and coatings to a wide variety of materials, includingpolymeric, metallic, and brittle materials. The technique provides aquantitative measure of adhesion in the form of the interfacial strainenergy release rate.

As disclosed in the examples of United States Patent ApplicationPublication No. 2004/0229444 A1, indentation measurements of siliconcoatings on glass can be performed using a Nano Indenter II (MTS SystemsCorporation, Eden Prairie, Minn.) equipped with a Berkovich diamondindenter. Other equipment can, of course, be used to determine bondstrength values. As discussed in detail in Example 12 of United StatesPatent Application Publication No. 2004/0229444 A1, indentations weremade covering a range of loads and the region immediately surroundingthe indentations was examined for evidence of delamination. Calculationsof bond energies were made in accordance with the following reference,the relevant portions of which are incorporated herein by reference: D.B. Marshall and A. G. Evans, Measurement of Adherence of ResiduallyStressed Thin Films by Indentation, I. Mechanics of InterfaceDelamination, J. Appl. Phys., 56 [10] 2632-2638 (1984). The proceduresof this reference are to be used in calculating the bond energies calledfor by the claims set forth below.

When the SOI structure is produced using the process according to thesecond aspect of the invention, the first layer will desirably have asurface farthest from the second layer which is an exfoliation surface.In this case, the oxide glass or oxide glass ceramic of the second layerwill also preferably have:

(a′) a 0-300° C. coefficient of thermal expansion CTE and a 250° C.resistivity ρ which satisfy the relationships:5×10⁻⁷/° C.≦CTE≦75×10⁻⁷/° C., and ρ≦10¹⁶ Ω·cm, and

(b′) a strain point T_(s) of less than 1,000° C.

The oxide glass or oxide glass ceramic will also comprise positive ionswhose distribution within the oxide glass or oxide glass-ceramic can bealtered by an electric field when the temperature T of the oxide glassor oxide glass-ceramic satisfies the relationship:T _(s)−350≦T≦T _(s)+350,where T_(s) and T are in ° C.

As will be appreciated, the strength of the bond between the glass orglass-ceramic layer and the semiconductor layer, e.g., silicon layer,attached thereto is a key property of an SOI structure. High bondstrength and durability are very important to ensure that the SOIstructure can withstand the processing associated with the manufactureof thin film transistors and other devices on or within the structure.For example, a high bond strength is important in providing deviceintegrity during cutting, polishing, and similar processing steps. Ahigh bond strength also allows semiconductor films of variousthicknesses to be processed while attached to glass or glass-ceramicsubstrates, including thin semiconductor films.

It is known that the bond energy for the Si—SiO₂ bond for the standardthermal process for producing SOI structures depends on the annealingtemperature and is in the range of 1-4 joules/meter² after a 1100° C.anneal. See Semiconductor Wafer Bonding, Q. Y. Tong, U. Gosele, JohnWiley & Sons Inc., New York, N.Y., page 108, (1994). As demonstrated bythe examples set forth in US 2004/0229444 A1, in accordance with thesecond aspect of the invention, bond strengths for SOI structures muchhigher than those previously achieved are provided, i.e., bond strengthsof at least 8 joules/meter².

In accordance with the process of the second aspect of the presentinvention, SOI structures having the following characteristics may beproduced:

I: A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers, wherein:

(a′) the first layer:

-   -   (i) comprises a substantially single-crystalline semiconductor        material;    -   (ii) has first and second substantially parallel faces separated        by a distance D_(S), the first face being closer to the second        layer than the second face;    -   (iii) has a reference surface which 1) is within the first        layer, 2) is substantially parallel to the first face, and 3) is        separated from that face by a distance D_(S)/2; and    -   (iv) has a region of enhanced oxygen concentration which begins        at the first face and extends towards the second face, said        region having a thickness δ_(H) which satisfies the        relationship:        δ_(H)≦200 nanometers,    -   where δ_(H) is the distance between the first face and a surface        which 1) is within the first layer, 2) is substantially parallel        to the first face, and 3) is the surface farthest from the first        face for which the following relationship is satisfied:        C_(O)(x)−C_(O/Ref)≧50 percent, 0≦x≦δ _(H),    -   where:    -   C_(O)(x) is the concentration of oxygen as a function of        distance x from the first face,    -   C_(O/Ref) is the concentration of oxygen at the reference        surface, and    -   C_(O)(x) and C_(O/Ref) are in atomic percent; and

(b′) the second layer comprises an oxide glass or an oxideglass-ceramic.

It should be noted that the region of enhanced oxygen concentration ofthis aspect of the invention is to be distinguished from an oxide layerformed on the outside of the semiconductor substrate prior to bonding(see, for example, U.S. Pat. No. 5,909,627) in that the region of thepresent invention is within the semiconductor material. In particular,when the SOI structure is produced using the process according to thesecond aspect of the invention, the region of enhanced oxygenconcentration is formed in situ as the composite of the semiconductorlayer and the oxide glass or oxide glass-layer is formed.

II: A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers, wherein:

(a′) the first layer comprises a substantially single-crystallinesemiconductor material, said layer having a surface farthest from thesecond layer which is an exfoliation surface; and

(b′) the second layer:

-   -   (i) has first and second substantially parallel faces separated        by a distance D₂, the first face being closer to the first layer        than the second face;    -   (ii) has a reference surface which 1) is within the second        layer, 2) is substantially parallel to the first face, and 3) is        separated from that face by a distance D₂/2;    -   (iii) comprises an oxide glass or an oxide glass-ceramic which        comprises positive ions of one or more types, each type of        positive ion having a reference concentration C_(i/Ref) at the        reference surface; and    -   (iv) has a region which begins at the first face and extends        towards the reference surface in which the concentration of at        least one type of positive ion is depleted relative to the        reference concentration C_(i/Ref) for that ion (the positive ion        depletion region).

III: A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers, wherein:

(a′) the first layer comprises a substantially single-crystallinesemiconductor material, said layer having a thickness of less than 10microns (in certain embodiments, less than 5 micron; in certain otherembodiments, less than 1 micron); and

(b′) the second layer:

-   -   (i) has first and second substantially parallel faces separated        by a distance D₂, the first face being closer to the first layer        than the second face;    -   (ii) has a reference surface which 1) is within the second        layer, 2) is substantially parallel to the first face, and 3) is        separated from that face by a distance D₂/2;    -   (iii) comprises an oxide glass or an oxide glass-ceramic which        comprises positive ions of one or more types, each type of        positive ion having a reference concentration C_(i/Ref) at the        reference surface; and    -   (iv) has a region which begins at the first face and extends        towards the reference surface in which the concentration of at        least one type of positive ion is depleted relative to the        reference concentration C_(i/Ref) for that ion (the positive ion        depletion region).

In connection with this SOI structure, it should be noted that the 10micron limitation of subparagraph (a′) is substantially less than thethickness of a semiconductor wafer. For example, commercially availablesilicon wafers generally have thicknesses greater than 100 microns.

IV: A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers, wherein:

(a′) the first layer comprises a substantially single-crystallinesemiconductor material; and

(b′) the second layer comprises an oxide glass or an oxide glass-ceramicwhich comprises positive ions of one or more types, wherein the sum ofthe concentrations of lithium, sodium, and potassium ions in the oxideglass or oxide glass-ceramic on an oxide basis is less than 1.0 weightpercent and, preferably, less than 0.1 weight percent (i.e., wt. %Li₂O+wt. % K₂O+wt. % Na₂O<1.0 wt. %, preferably, <0.1 wt. %),

wherein the first layer has a maximum dimension (e.g., diameter in thecase of a circular layer, diagonal in the case of a rectangular layer,etc.) greater than 10 centimeters.

V: A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers, wherein:

(a′) the first layer comprises a substantially single-crystallinesemiconductor material; and

(b′) the second layer:

-   -   (i) has first and second substantially parallel faces separated        by a distance D₂, the first face being closer to the first layer        than the second face;    -   (ii) has a reference surface which 1) is within the second        layer, 2) is substantially parallel to the first face, and 3) is        separated from that face by a distance D₂/2;    -   (iii) comprises an oxide glass or an oxide glass-ceramic which        comprises positive ions of one or more types, each type of        positive ion having a reference concentration C_(i/Ref) at the        reference surface;    -   (iv) has a region which begins at the first face and extends        towards the reference surface in which the concentration of at        least one type of positive ion is depleted relative to the        reference concentration C_(i/Ref) for that ion (the positive ion        depletion region), said region having a distal edge (i.e., the        edge closest to the reference surface); and    -   (v) has a region in the vicinity of said distal edge of the        positive ion depletion region in which the concentration of at        least one type of positive ion is enhanced relative to C_(i/Ref)        for that ion (the pile-up region).

VI: A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers with a bond strength of at least 8joules/meter, in certain embodiments at least 10 joules/meter², and incertain embodiments at least 15 joules/meter², said first layercomprising a substantially single-crystalline semiconductor material andsaid second layer comprising an oxide glass or an oxide glass-ceramicwherein at least a portion of the first layer proximal to the secondlayer comprises recesses which divide said portion into substantiallyisolated regions which can expand and contract relatively independentlyof one another.

In certain embodiments of this SOI structure, the recesses extendthrough the entire thickness (D_(S)) of the first layer.

VII: A silicon-on-insulator structure comprising first and second layerswhich are directly attached to one another, said first layer comprisinga substantially single-crystalline silicon material and said secondlayer (20) comprising a glass or a glass-ceramic which comprises silicaand one or more other oxides as network formers (e.g., B₂O₃, Al₂O₃,and/or P₂O₅), said first layer comprising a region which contacts thesecond layer and comprises silicon oxide (i.e., SiO_(x) where 1≦x≦2) butdoes not comprise the one or more other oxides, said region having athickness which is less than or equal to 200 nanometers.

VIII: A semiconductor-on-insulator structure comprising a substantiallysingle-crystalline semiconductor material (material S) and an oxideglass or an oxide glass-ceramic which comprises positive ions (materialG), wherein at least a part of the structure comprises in order:

material S;

material S with an enhanced oxygen content;

material G with a reduced positive ion concentration for at least onetype of positive ion;

material G with an enhanced positive ion concentration for at least onetype of positive ion; and

material G.

In connection with each of the foregoing SOI structures I-VIII, andadditional SOI structures described infra, that can be producedaccording to the process of the second aspect of the present invention,it should be noted that the “insulator” component of asemiconductor-on-insulator structure is automatically provided by theinvention through the use of an oxide glass or an oxide glass-ceramic asthe second substrate. The insulating function of the glass orglass-ceramic is even further enhanced when the interface (30) betweenthe first and second substrates includes a positive ion depletionregion. As a specific example, in the SOI structure VIII, all of the Gmaterials are insulators. In addition, the S material with enhancedoxygen concentration may, at least to some extent, function as aninsulator depending on the oxygen concentration achieved. In such cases,everything after the S material constitutes the insulator of the SOIstructure. It should also be noted that the single-crystallinesemiconductor materials may be also be doped with dopants at variouslevels, e.g., for the purpose of imparting semiconductive properties.

This automatic provision of the insulator function in accordance withthe invention is to be contrasted with conventional SOI structures inwhich a semiconductor film is attached to a semiconductor wafer. Toachieve an insulating function, an insulator layer, e.g., a SiO₂ layer,needs to be sandwiched (buried) between the semiconductor film and thesemiconductor wafer.

In accordance with the second aspect of the invention, the methods ofthe present invention can be practiced to produce multiple SOIstructures on a single oxide glass or oxide glass-ceramic substrate,where the SOI structures may all be the same, all different, or some thesame and some different. Similarly, the products resulting from thesecond aspect of the present invention can have multiple first layers ona single second layer, where again, the first layers may all be thesame, all different, or some the same and some different.

Whether a single first layer or a plurality of first layers are used,the resulting SOI structure can either have all or substantially all(i.e., >95%) of the first face of the second layer attached (eitherdirectly or through one or more intermediate layers) to one or morekinds of substantially single-crystalline semiconductor materials, orcan have substantial areas of the first face that are associated withmaterials that are not substantially single-crystalline semiconductormaterials (hereinafter, the “non-single-crystalline semiconductorareas”).

In the non-single-crystalline semiconductor areas, the first face can beattached, either directly or through one or more intermediate layers,to, for example, amorphous and/or polycrystalline semiconductormaterials, e.g., amorphous and/or polycrystalline silicon. The use ofsuch less expensive materials can be particularly beneficial in displayapplications where substantially single-crystalline semiconductormaterials are typically only needed for certain parts of the displayelectronics, e.g., for peripheral drivers, image processors, timingcontrollers, and the like, that require higher performance semiconductormaterials. As well-known in the art, polycrystalline semiconductormaterials and, in particular, polycrystalline silicon can be obtained bythermal crystallization (e.g., laser-based thermal crystallization) ofamorphous materials after those materials have been applied to asubstrate, such as, an LCD glass substrate.

The entire first face of the second layer, of course, does not have tobe associated with substantially single-crystalline ornon-single-crystalline semiconductor materials. Rather, specified areascan have the semiconductor materials with the spaces between such areasbeing either bare second layer or second layer attached to one or morenon-semiconductor materials. The sizes of such spaces can be large orsmall as appropriate to the particular application of the invention. Forexample, in the case of display applications, e.g., liquid crystaldisplays, the great majority of the glass layer (e.g., greater thanapproximately 75-80%) will typically not be associated with eithersubstantially single-crystalline or non-single-crystalline semiconductormaterials.

Through the use of multiple first layers attached to a single secondlayer, SOI structures having extensive areas composed of substantiallysingle-crystalline semiconductor materials can be obtained. Thus, inaccordance with the process of the second aspect of the presentinvention, the following additional SOI structures can be produced:

IX. A semiconductor-on-insulator structure comprising first and secondlayers which are attached to one another either directly or through oneor more intermediate layers, wherein:

(a′) the first layer comprises a plurality of regions each of whichcomprises a substantially single-crystalline semiconductor material;

(b′) the second layer comprises an oxide glass or an oxideglass-ceramic; and

(c′) the regions have surface areas Ai which satisfy the relationship:

${{\sum\limits_{i = 1}^{N}A_{i}} > A_{T}},{N > 1},$where A_(T)=750 centimeters² if any of the regions has a circularperimeter and A_(T)=500 centimeters² if none of the regions has acircular perimeter.

As above, the substantially single-crystalline semiconductor materialsof the various regions can all be the same, all different, or some thesame and some different. Similarly, if one or more intermediate layersare used, they can all be the same, all different, or some the same andsome different for the various regions. In particular, one or moreregions can have the substantially single-crystalline semiconductormaterial attached to the second layer through one or more intermediatelayers, while one or more other regions can have the semiconductormaterial attached directly to the second layer.

In connection with the foregoing SOI structures I-IX that may beproduced according to the process of the second aspect of the presentinvention, the one or more intermediate layers between the first andsecond substrates, if present, preferably have a combined thickness ofless than 100 nm, in certain embodiments less than 50 nm, and certainembodiments, less than 30 nm.

In addition to the above-listed individual SOI structures I-IX, theprocess of the second aspect of the present invention may also be usedto produce SOI structures comprising any and all combinations of thecharacteristics of I-IX. For example, certain embodiments of the SOIstructures may preferably have a bond strength of at least 8joules/meter, in certain embodiments preferably at least 10joules/meter², and in certain embodiments most preferably at least 15joules/meter. Similarly, the SOI structure may preferably includes atleast one exfoliation surface, at least one positive ion depletionregion, at least one pile-up region, and/or a semiconductor layer whosethickness is less than 10 microns.

The present invention is further illustrated by the followingnon-limiting examples.

EXAMPLES Example 1 Comparative Example

A silicon wafer 150 mm diameter, 500 microns thick was H₃ ⁺ion-implanted at dosage of 2E16 (i.e., 2×10¹⁶) H₃ ⁺ ions/cm² andimplantation energy of 60 KeV in a standard unmodified, conventional ionshower equipment. The wafer was then treated in oxygen plasma to oxidizethe surface groups. A Corning Incorporated Eagle 2000™ glass wafer 100mm in diameter was then washed with Fischer scientific Contrad 70detergent in ultrasonic bath for 15 minutes followed by distilled waterwash for 15 minutes in ultrasonic bath and then washed in 10% nitricacid followed by distilled water wash again. Both these wafers werefinally cleaned in spin washer dryer with distilled water in the cleanroom.

The two wafers were then brought into contact ensuring that no air wastrapped between the wafers and then the wafers were introduced into thebonder and bonded as taught in US 2004/0229444 A1. The glass wafer wasplaced on the negative electrode and the silicon wafer was placed on thepositive electrode. The two wafers were heated to 525° C. (siliconwafer) and 575° C. (glass wafer). A potential of 1750 Volts was appliedacross the wafer surface. The voltage was applied for 20 minutes at theend of which the voltage was brought to zero and the wafers were cooledto room temperature. The wafers could be separated easily. TEM image wastaken of the cross-section of the exfoliated silicon film. An image ispresented in FIG. 7, which shows that the silicon film was damagedthroughout the thickness making the silicon film of little use for theelectronics applications.

Example 2 The Present Invention

The experiment of Example 1 is being repeated with the same experimentalparameters but in a tool containing an analyzer magnet which allows massseparation and thus allows implantation of only the desired species H₃⁺. This is expected to result in a silicon film with damage confinedessentially only to the fracture zone which may be removed by polishingor etching revealing a good undamaged silicon layer useful forelectronic devices. Additional experiments H₃ ⁺ followed by He⁺ ionimplantation is expected to produce similar results as well.

It will be apparent to those skilled in the art that variousmodifications and alterations can be made to the present inventionwithout departing from the scope and spirit of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A process for forming a SOI structure comprising the following steps:(I) providing a donor substrate comprising semiconductor material havinga first donor external surface; and (II) implanting a plurality of ionsbelonging to a first species through the first donor external surfaceinto an ion implantation zone at a depth below the first donor externalsurface by using a first ion shower purified by electromagneticseparation effected by magnetic means such that the structure of atleast a 50 nm thick part of the material sandwiched between the ionimplantation zone and the first donor external surface (“exfoliationfilm”) is essentially not damaged.
 2. A process according to claim 1,wherein in step (II), at least a 100 nm thick part, in certainembodiments at least a 150 nm thick part, in certain embodiments atleast a 200 nm thick part, of the exfoliation film is essentially notdamaged.
 3. A process according to claim 1, wherein the exfoliation filmcomprises single crystalline silicon.
 4. A process according to claim 1,wherein in step (II), the ion implantation zone has a thickness of notlarger than about 1 μm, in certain embodiments not larger than about 500nm, in certain other embodiments not larger than about 300 nm, incertain other embodiments not larger than about 200 nm.
 5. A processaccording to claim 1, wherein in step (II), the depth of the ionimplantation zone is less than about 1000 nm, in certain embodimentsless than about 500 nm, in certain other embodiments less than about 300nm, in certain other embodiments less than about 150 nm, in certainother embodiments less than about 100 nm.
 6. A process according toclaim 1, wherein the thickness of the non-damaged part of theexfoliation film is at least 50% of the total thickness of theexfoliation film, in certain embodiments at least 60% of the totalthickness of the exfoliation film, in certain embodiments at least 80%of the total thickness of the exfoliation film, in certain embodimentsat least 90%.
 7. A process according to claim 1, wherein at least oneof: in step (II), the first ion shower consists essentially of the ionsbelonging to a first species; the ions belonging to the first species isa single ion species selected from H₃ ⁺, H⁺, H₂ ⁺, D₂ ⁺, D₃ ⁺, HD+,H₂D⁺, HD₂ ⁺, He⁺, He²⁺, O⁺, O₂ ⁺, O²⁺ and O₃ ⁺; and the ions belongingto the first species are essentially free of phosphorous, boron,arsenic, carbon, oxygen, nitrogen, fluorine, chlorine and metals.
 8. Aprocess according to claim 1, further comprising the following step(IIIB) separate from and independent of step (II): (IIIB) implanting aplurality of ions through the first donor external surface into the ionimplantation zone at the depth below the first donor external surface byusing a conventional ion shower.
 9. A process according to claim 1,further comprising at least one of: (IV) bonding the first donorexternal surface to a recipient substrate; and (V) separating theexfoliation film and at least part of the material in the ionimplantation zone from the donor substrate at a location within theimplantation zone.
 10. A process according to claim 9, wherein therecipient substrate is selected from the group consisting of: asemiconductor wafer with or without an oxide surface layer; a glassplate; plate comprised of crystalline material and a glass-ceramicplate.
 11. A process according to claim 9, wherein at least one of: therecipient substrate is a silicon wafer with a SiO₂ surface layer, andthe first donor external surface of is bonded to the SiO₂ surface layerin step (IV); and the recipient substrate is a SiO₂ glass plate.
 12. Aprocess according to claim 9, wherein: (1) the recipient substratecomprises oxide glass or oxide glass-ceramic; and (2) in step (IV), thebonding is effected by applying (a) forces to the donor and recipientsubstrates such that they are pressed into close contact; (b) electricalfield within the donor and recipient substrates such that the electricalpotential in the donor substrate is higher than that in the recipientsubstrate; and (c) a temperature gradient between the donor andrecipient substrates.
 13. A process for forming a SOI structurecomprising the following steps: (A1) providing a donor substrate and arecipient substrate, wherein: (1) the donor substrate comprises asemiconductor material and a first donor external surface for bondingwith the recipient substrate (first bonding surface) and a second donorexternal surface; (2) the recipient substrate comprises an oxide glassor oxide glass-ceramic and two external surfaces: (i) a first recipientexternal surface for bonding to the first substrate (the second bondingsurface); and (ii) a second recipient external surface; (A2) implantinga plurality of ions belonging to a first species through the first donorexternal surface into an ion implantation zone of the donor substrate ata depth below the first donor external surface by using a first onshower purified by, electromagnetic separation effected by magneticmeans such that the internal structure of at least a 50 nm thick part ofthe film of material sandwiched between the ion implantation zone andthe first donor external surface (“exfoliation film”) is essentially notdamaged; (B) after steps (A1) and (A2), bringing the first and secondbonding surfaces into contact; (C) for a period of time sufficient forthe donor and recipient substrates to bond to one another at the firstand second bonding surfaces, simultaneously: (1) applying forces to thedonor substrate and/or the recipient substrate such that the first andsecond bonding surfaces are pressed into contact; (2) subjecting thedonor and recipient substrates to an electric field having a generaldirection of from the second recipient external surface to the seconddonor external surface; and (3) heating the donor and recipientsubstrates, said heating being characterized in that the second donorand recipient external surfaces have average temperatures T₁ and T₂,respectively, said temperatures being selected such that upon cooling toa common temperature, the donor and recipient substrates undergodifferential contraction to thereby weaken the donor substrate at theion implantation zone; and (D) cooling the bonded donor and recipientsubstrates and splitting the donor substrate at the ion implantationzone; wherein the oxide glass or oxide glass-ceramic comprises positiveions which during step (C) move within the recipient substrate in adirection away from the second bonding surface and towards the secondrecipient external surface.
 14. A process according to claim 13, whereinin step (A2), the structure of at least a 100 nm thick part, in certainembodiments at least a 150 nm thick part, in certain embodiments atleast a 200 nm thick part, of the exfoliation film is not damaged.
 15. Aprocess according to claim 13, wherein at least one of the exfoliationfilm comprises single crystalline semiconductor material; and theexfoliation film comprises single crystalline silicon.
 16. A processaccording to claim 13, wherein in step (II), the depth of the ionimplantation zone is less than about 1000 nm, in certain embodimentsless than about 500 nm, in certain other embodiments less than about 300nm, in certain other embodiments less than about 150 nm, in certainother embodiments less than about 100 nm.
 17. A process according toclaim 13, wherein the thickness of the non-damaged part of theexfoliation film is at least 50% of the total thickness of theexfoliation film, in certain embodiments at least 60% of the totalthickness of the exfoliation film, in certain embodiments at least 80%of the total thickness of the exfoliation film, in certain embodimentsat least 90%.
 18. A process according to claim 13, wherein in step (A2),the ion implantation zone has a thickness of not larger than about 1 μm,in certain embodiments not larger than about 500 nm, in certain otherembodiments not larger than about 300 nm, in certain other embodimentsnot larger than about 200 nm.
 19. A process according to claim 13,wherein at least one of: in step (A2), the first ion shower consistsessentially of the ions belonging to a first species; the ions belongingto the first species is a single ion species selected from H₃ ⁺, H⁺, H₂⁺, D₂ ⁺, D₃ ⁺, HD⁺, H₂D⁺, HD₂ ⁺, He⁺, He²⁺, O⁺, O₂ ⁺, O²⁺ and O₃ ⁺; andthe ions belonging to the first species are essentially free ofphosphorous, boron, arsenic, carbon, oxygen, nitrogen, fluorine,chlorine and metals.
 20. A process according to claim 13, wherein afterstep (A2) but before step (B), the first bonding surface of the donorsubstrate is treated to reduce the hydrogen concentration thereof.
 21. Aprocess according to claim 20, wherein thehydrogen-concentration-reducing treatment causes the first bondingsurface to be hydrophilic.
 22. A process according to claim 20, whereinthe hydrogen-concentration-reducing treatment is selected from oxygenplasma treatment, ozone treatment, treatment with H₂O₂, treatment withH₂O₂ and ammonia, treatment with H₂O₂ and an acid, and combinationsthereof.